The present invention relates to a method for manufacturing a laser diode with a buried active layer.
It is known to manufacture laser diodes with low threshold currents and high output power as a laser diode having a double hetero layer structure and a buried active layer (see, for example, G. Winstel, C. Weyrich, Optoelektronik 1, Springer Verlag, Berlin, Heidelberg, New York 1980, pages 225 through 232). The active layer is embedded in the form of a stripe in a semiconductor material that has a lower refractive index and a higher energy band gap than the material of the active layer. Due to the different cut-off voltages of the homo-pn junctions at the side of the active layer and of the hetero-pn junction of the active layer, the current essentially flows over the active layer.
To improve the lateral current conduction at least one blocking pn-junction is respectively arranged at the side of the active layer. These blocking pn-junctions are usually integrated in a second epitaxial process, whereby the method is designed such that no such blocking junction is obtained above the active laser stripe.
It is known to prevent the growth of a blocking junction on the active stripe by applying masking layers such as, for example, SiO.sub.2 or on the basis of the selection of the profile of the active stripe, whereby what is thereby exploited is that no crystal growth ensues on the surface of the stripe on specific crystal faces or given specific relationships of height and width of the stripe. A further possibility is to initially grow the blocking pn-junction over the active stripe as well and to then render it conductive again by selective diffusion. Masking layers such as, for example, SiO.sub.2 must be dissolved again in a separate work cycle. The impossibility of crystal growth on specific crystal faces and stripe shapes limits the selection of the stripe profile. Selective diffusion makes additional method steps necessary.